1. Field of the Invention
The present invention relates to a method of marking marks on a metallic layer, and a metallic layer with marks and a semiconductor device having the metallic layer, in more detail, relates to a method of marking marks (emblem) such as characters, codes, patterns or the like by illuminating a laser beam on a surface of a metallic layer, a metallic layer with marks thereon, and a semiconductor having a metallic layer with marks thereon.
2. Description of Related Art
So far, as a method of marking marks such as characters, codes, patterns or the like on a surface of a metallic member in order to indicate product names, product specifications, logotypes, product lot numbers or the like, such as shown in FIG. 6, a laser marking method of illuminating a laser beam 2 on a surface of a metallic layer 1 is known. According to this method, the energy of the illuminated laser beam 2 sublimes metal particles or spatters metallic debris 3 from the surface of the metallic layer 1 to dig concave portions thereon, the dug portions 4 being the marking portions.
However, in the case of applying such so far employed marking method to a metallic member in which an underlying metallic layer is covered by a thin metallic plating layer, due to illumination of a laser beam 2, a part or all of the plating layer is removed. Here, since corrosion reaction such as oxidation or the like occurs due to exposure of the underlying metal, there is a problem such as deterioration of visibility occurs.
In a BGA (ball grid array) type semiconductor device having a heat-radiating cover plate, for instance, though a cover plate covered by a nickel plating layer (thickness of 2 to 10 xcexcm) is disposed on a surface of a copper plate for preventing from rusting, in the case of carrying out marking by conventional illumination of a laser beam on such a cover plate, the nickel plating layer is removed to expose the underlying copper layer, due to corrosion of copper, the visibility of the dug portions 4 is deteriorated.
Further, in the conventional method, the marking is carried out by deleting the surface of the metallic layer 1, air contaminating substances such as metallic debris 3 or metal particles are generated, accordingly measures such as dust collection or the like were necessary. Further, there is a troublesome problem such that, in order for the generated and floating metallic debris 3 or the like not to interrupt the laser beam 2, digging operation is required to be carried out while evacuating/removing these floating materials by a suction pump.
The present invention was carried out to solve these problems. That is, an object of the present invention is to provide a marking method which, by illuminating a laser beam on a surface of a metallic layer, forms marks of excellent visibility, and does not generate air-contaminating materials such as metallic debris or the like, a metallic layer with marks of excellent visibility, and a semiconductor device having a metallic layer with such marks.
A method of marking on a metallic layer of the first invention of the present invention illuminates a laser beam on a predetermined marking area of a metallic layer having the maximum surface roughness (Rmax) of 0.5 to 5 xcexcm, thereby melts a neighboring area of the surface of the metallic layer and then solidifies again the area, thus forms a marking portion having different light reflectivity from the underlying portion of the metallic layer.
A metallic layer with a mark of the second invention of the present invention comprises an underlying portion having the maximum surface roughness (Rmax) of 0.5 to 5 xcexcm, and a marking portion having different light reflectivity from that of the underlying portion.
Further, a semiconductor device of the third invention of the present invention comprises the aforementioned metallic layer with marks.
In the marking method of the present invention, the surface of the metallic layer thereon the laser beam is illuminated is a matte surface (non-glossy surface) having minute unevenness, the surface roughness being 0.5 to 5 xcexcm by the maximum value (Rmax). In the case of the maximum surface roughness (hereinafter refers to as Rmax) being out of the aforementioned range, scattering property on the surface of the underlying portion which is a non-marking portion becomes insufficient. Since the difference of the light reflectivity from that of the marking portion formed by the illumination of a laser beam becomes small, the visibility of the marking portion becomes insufficient. The more preferable Rmax is in the range of 1 to 3 xcexcm.
Further, in the method of the present invention, as a method of illuminating a beam of laser only on a predetermined marking area, there is an imaged-mask laser system which illuminates a laser beam through an exposing mask having a predetermined pattern, or a steered-beam laser writing system in which a focused point of the laser beam is scanned continuously by use of computer-driven mirrors mounted on galvanometers. In the steered-beam laser writing system, by moving 2 prisms (or reflecting mirrors) for transferring in X-axis direction and in Y-axis direction, respectively, by a linear motor each, the laser beam is scanned in parallel with the X-axis and Y-axis directions with excellent accuracy.
In the method of the present invention, on a marking area of a surface of a metallic layer having various sizes of unevenness with the Rmax of 0.5 to 5 xcexcm, a laser beam of such as a YAG laser or the like is illuminated, thereby the neighborhood of the surface of the metallic layer of the marking area is melted by the energy of the laser and solidified again thereafter. The surface of the marking area thus melted and solidified thereafter, though there remaining the waviness (swelling) of large wavelength, gives a smooth surface in which the minute unevenness of 0.1 to 0.3 xcexcm is leveled and erased. And, as shown in FIG. 1A enlarged, this smooth surface 5 reflects specularly an incident light 6 in one direction according to the law of reflection. On the other hand, the surface of the underlying portion other than the marking area of the metallic layer, as shown in FIG. 1B, is a matte surface 7 of various sizes of unevenness, accordingly the beams of the incident light 6 are scattered evenly in all directions (diffuse reflection). Therefore, due to such a difference in reflectivity of light, as a dark part formed in the underlying portion which is seen bright (white) from any directions, the marking area can be seen with high contrast.
Since formation of the marking area of the present invention is carried out according to such the principle, illumination energy of the laser beam is set at the degree which is necessary and sufficient to melt the metallic layer in an appropriate time period (relatively slowly). When the energy of the laser beam is illuminated too much, the surface of the metallic layer is rapidly melted to erupt, thereby a concave portion like a crater of a large diameter and of depth is formed on the marking portion, and on the circumference of the concave a swelling portion like a milk crown is formed. Accordingly, the visibility and quality of the marking area deteriorate. The preferable condition for laser illumination, in the case of illuminating a Q-switched YAG laser according to a scanning method for instance, is in the range of 10 to 44W for the laser output and in the range of 100 to 600 mm/s for the scanning speed.
Thus, since the marks formed according to the method of the present invention are excellent in its contrast with respect to the surrounding underlying portion, not only it can be seen readily by the naked eyes but also it can be discerned by an image recognition device. By adjusting the illuminating energy of the laser, being melted with an adequate speed without digging/cutting or rapidly melting the metallic layer, even on a thin metallic plating layer, a mark of excellent visibility and quality can be formed.
Further, according to such the method of the present invention, marks are formed by melting a metallic layer, accordingly there is no occurrence of the air contaminant such as metallic debris during marking and workability is excellent.